Allow customize error message

[dartess]

Now I get standard message like Try to reduce size or increase limit at .size-limit.json.

It would be great to be able to change this message, including setting a different message for different groups of files, like this:

  "size-limit": [
    {
      "path": "main.js",
      "limit": "500 ms",
      "message": "Call Hugo"
    },
    {
      "path": "page-index-*.js",
      "limit": "100 ms",
      "message": "Call Ghostbusters"
    },
  ]

[ai]

Please send PR